Described herein is the development of drugs that target two hallmarks of disease, including cancer, the loss of cell cycle checkpoint control (1) and abnormal glycosylation (2, 3). Uncontrolled cell proliferation characteristic of transformed cells is, at least in part, epigenetic in origin and results from cancer-specific anomalies in chromatin structure (4, 5). Chromatin consists of DNA, histones, and accessory proteins such as histone deacetylase (HDAC) and histone acetyltransferase (HAT). Together, HDAC and HAT remodel chromatin to provide a “code” that is recognized by the non-histone proteins that regulate gene expression (4). Not surprisingly, there is growing interest in the precise mechanisms that regulate chromatin remodeling with the bulk of these efforts focused on the inhibition of histone deacetylase (HDAC) activities. In recent years, the ability of HDAC inhibitors (HDACi) to disrupt the cell cycle or selectively induce apoptosis via de-repression of genes such as P21 and BAX in cancer cells, has made HDAC inhibition an attractive avenue for drug development (6) and intense efforts are underway to develop clinically-relevant HDACi for cancer therapy (7, 8).
In addition to epigenetic modifications, tumorigenesis frequently involves abnormal glycosylation that alters cell surface properties. These changes to the cell surface underlie altered cell adhesion and trigger abnormal inter- and intra-cellular signaling that simulate cell proliferation and metastasis. Examples of altered cell adhesion which contribute to metastasis include an initial decrease in adhesion that allows a malignant cell to break free of the primary tumor and a later increase in adhesion that allows a circulating cell to adhere to the vessel and extravasate into another tissue. Glycosylation, in particular sialylation, influence the changing adhesive properties of metastatic cells. Abnormal glycosylation also alters the interaction of cell-surface signaling molecules and produces abnormal inter- and intra-cellular signaling. For example, altered glycosylation of integrin influences its associations with other cell surface molecules. Therapies that disrupt the abnormal glycosylation of cancer cells might inhibit cell proliferation and metastasis.
n-Butyrate, a naturally-occurring HDACi belonging to the class of compounds known as short chain fatty acids (SCFAs) (9) has the attractive property of inducing cell cycle arrest and apoptosis in transformed cells while leaving healthy cells unharmed by reactivating cell cycle check point proteins such as p21WAF1, a cyclin-dependent kinase inhibitor (10). Efforts to exploit n-butyrate for clinical treatment of cancer, however, have been stymied by its poor pharmacological properties and the high levels (up to 50 mM) needed for bioactivity (11). One approach to avoid the pharmacokinetic limitations of butyrate has been to use traditional enzyme-substrate screening assays to discover “drug-like” small molecule HDACi such as trichostatin (TSA), suberoyl hydroxamic acid (SAHA), and MS-275 among others (7). These compounds inhibit cell growth, induce terminal differentiation, and prevent tumor formation in animal models (12). Despite these attractive anti-cancer properties and nanomolar binding affinities to HDAC when tested against purified enzyme, the majority of current HDACi clinical candidates require unrealistically high (up to millimolar) concentrations to be effective against cells (4).